1. Field of the Invention
This invention relates generally to the field of medical monitoring devices, and more particularly relates to medical devices used to detect low amplitude artifacts produced by artificial cardiac pacing.
2. Description of the Prior Art
A wide variety of cardiac pacemakers are known and commercially available. Pacemakers are generally characterized by which chambers of the heart they are capable of sensing, the chambers to which they deliver pacing stimuli, and their responses, if any, to sensed intrinsic electrical cardiac activity. Some pacemakers deliver pacing stimuli at fixed, regular intervals without regard to naturally occurring cardiac activity. More commonly, however, pacemakers sense electrical cardiac activity in one or both of the chambers of the heart, and inhibit or trigger delivery of pacing stimuli to the heart based on the occurrence and recognition of sensed intrinsic electrical events. A so-called "SSI" pacemaker, for example, senses electrical cardiac activity in a chamber, atrium (A) or ventricle (V), of the patient's heart, and delivers pacing stimuli to the same chamber only in the absence of electrical signals indicative of natural chamber contractions. A "DDD" pacemaker, on the other hand, senses electrical signals in both the atrium and ventricle of the patient's heart, and delivers atrial pacing stimuli in the absence of signals indicative of natural atrial contractions, and ventricular pacing stimuli in the absence of signals indicative of natural ventricular contractions. The delivery of each pacing stimulus by a DDD pacemaker is synchronized with prior sensed or paced events.
Pacemakers are also known which respond to other types of physiological based signals, such as signals from sensors for measuring the pressure inside the patient's ventricle or measuring the level of the patient's physical activity. These devices are labeled "SSIR" for a single chamber version or "DDDR" for a dual chamber version.
As pacemaker technology as well as integrated circuit and lead technologies have evolved, chronic pacing thresholds have approached very low values (&lt;&lt;1.0 volts) and very efficient low current CMOS amplifier designs have become available. What is needed, but still missing in the art of pacing artifact detection however, is an isolation amplifier capable of driving biopotential signals across an isolation barrier at high frequencies above 200 kHz with little or no distortion, substantially higher than frequencies approaching about 70 kHz presently available in the art of pacing artifact detection. Such an amplifier will allow use of software correlators on the pacing artifact which has heretofore been unknown in the art of pacing artifact detection.